Instantaneously acting pneumatic timer



States Patent r g 2,904,073 v INSTANTANEOU SLY ACTING PNEUMATIC TIMER vRobert C'owlierd, West Terre Haute, Ind. ApplicationNovember 27, 1957,Serial No. 699,238 j (Ch l y 620).

This invention relates to a pneumatically actuated timing device that ischaracterized by snap-acting load energizing and de-energizing features.

Electric controls, such as solenoids, information net works, relay's,timers, etc., cannot be either economically of safely used in areaswhere explosive vapors or gases exist. Optimum installations of theseelectrical com- Fig. 1 illustrates atypical exponential time-pressurecurve A for a pneumatic system which includes air under pressure passingthrough a measured constriction into a closed system of finite volume.The curve B represents a time pressure curve for air under pressurepassing from a closed system 'offinite volume, through a measuredrestriction to atmosphere. a

Referring to Fig. 2, the valves there shown aregenerally. of a similarconstruction, and, referring to valve A in particular, include themovable valve member 3 traveling between valve seats 4. and 5. Actuationof the valve is eflected by a diaphragm 6 connected through a push rod 7to the valve member 3 and communicating at its upper surface or topwith'a duct, such as conduit 8. A spring 9 biases the valve in onedirection, oppositely to'the pressure exerted by the diaphragm. Thecommon port '10 of the valve will communicate with either ports 11 orIn, depending upon the presence or absence of pneumatic pressure at thevalve ltop.

Referring again to Fig; 1, and keeping in mind the construction of valveA, it can be assumedthat when the pressure in the valve top reaches avalue a the force exerted by the diaphragm 6 is exactly balanced by theinitial upward force created by spring 9. When the pressure on diaphragm6 reaches a value a the force on the diaphragm will not only overcomethe upward force exerted by spring 9, but'will cause the valve member 3ated valves utilize springs, which members cause them I x to throttle ormove proportional to the pressure applied to their actuators, ratherthan to. move in a snap acting manner.

An object of the present invention is, therefore, to provide an improvedcontrol system employing fluid-actuated valves with a view tosubstantially eliminating the throtfling of the valve operators.

More specifically, the object of this invention is to provide a timingcircuit consisting of an adjustable orifice,

a parallel connected volume and a suitable combination of pilot valvesthat will produce an instantaneous regenerativepressure and aninstantaneous deenergized reduction in pressure of an extemallyconnected load, which may take the form of a process control valve, acylinder actuator orother portions of an associated pneumatic circuit.

The nature of the invention will be understood from the accompanyingdrawings and the following description and claims:

Fig. 1 diagrammatically illustrates time pressure curves which arecharacteristic of a resistance-capacity combinationof elements.

Fig. 2 is a schematic diagram of a pneumatic control system embodyingthe present invention.

Fig. 3 is a diagrammatical illustration of the time pressure curves forcertain of the components in the system of Fig. 2.

Fig. 4 is a time-pressure chart indicating the pressure at one of theload connections of the system in Fig. 2.

Fig. '5 is a time-pressure chart indicating the pressure at a furtherone 'of the load connections shown in Fig. 2.

Fig. 6 is a time-pressure chart of a further l'oad con nection shown inFig. 2.

Fig. 7 is a chart indicating the positions of the various "valves duringeach step of an operating cycle.

While the invention will be herein described with reference-lto apneumatic system, it is not to be restricted to pneumatic systems alone.By making certain simple modifications, the circuit will allow the useof an incompressible fluid-or liquid.

to traverse the distance between seats 4 and 5. The difference betweenthe pressures a and a constitutes a range of pressure wherein valvemember 3 may be at some intermediate position between the seats 4 and 5.This pressure range, associated with valves of this type, produces aregulating or throttling action instead of a snap action. The system tobe subsequently described with reference to Fig. 2 provides a timingmechanism to provide the snap action effect.

Referring to Fig. 2, it may be assumed that the manifold or header 1 issupplied by a constant regulated pressure source capable of maintainingthe pneumatic pressure within the manifold within a few percent of apredetermined level. Twenty-five pounds per square inch is typical ofone source pressure commonly used in indus trial control circuits.

In the system of Fig. 2, the diaphragm top of a process valve H iscoupled intothe control system. Operation of the valve by the systemwill provide non-throttling or on- 051 control of the medium flowingthrough the process v ve.

, Let it be assumed that the time sequence shall be initiated bymomentarily depressing the push rod on'valve 20. The normally closedseat 27 is opened and the normally open seat 28 is closed,therebyadmitting a pulse of pressure from the port 21 which travelsthrough the port 12 or pilot valve'A, thence through common port 10.From the common port 10 of pilot valve A the pulse is connected throughnormally openlvalve seat :22 of pilot valve E, thence through the commonport 23 to the diaphragms of valves A and B. When the pressure wavereaches the actuation valve for the pilot valve' A, the seat 'Sclosesand the seat 4 opens. This actio'njof pilot valve A closes off theinitial air pulse from the portal of the push button 20, and by 'Way ofthe now openport 11 and the seat 4 admits an auxiliary source ofpressure to the di'aphrag'ms of pilot valves A and B. The/push rod onthe mechanism 20 may nowbe released without disturbin'g the pressuredcondition of the diaphragm-of valves Aand B. It will be noted that theforegoing has described the-exact pneumatic equivalentto the'mbmentaryenergization of "an electrical hold-in circuit, sometimes re-Ierredto a'sa' lock tip.- .AWhen .pilot valve B. isactuated, itsnormally opened seat closes; Pressure is, therefore, admitted to thediaphragms of pilot valves C and D, to the normally closed seat of pilotvalve F, and to the up-stream side of an adjustable restriction ororifice generally indicated at 24. Since'the normally open seat of pilotvalv'e B has previously been closed, the reversal of the seats of pilotvalve C will have 'no immediate effect on the system pressured by thenow open normally closed seat of pilot valve B. When thepilot valveD isactuated, its normally open seat is closed so that the circuitdown-stream from the adjustable restriction 24 becomes a closed volumewhich, in combination with the restriction 24, forms a resistancecapacity time constant system. At this point in the sequence, a timedelay has been initiated at the end of which the process 'valv e'H willbe instantaneously energized.

Air may now be effectively metered through the restriction 24 and,depending on the flow area of the restriction and the down-stream systemvolume, the pressure on the diaphragm of pilot valves G, E and F willincrease exponentially following curve A of Fig. 1, or along the line BCof Fig. 3. When the pressure in the now closed volume downstream fromthe adjustable restriction 24 reaches a value indicated at a in Fig. 3,pilot valves E, F and Gwill just being to overcome the force exerted bytheir respective loading springs. In particular, pilot F will be soaffected.

When the pressure on the diaphragm of valve F slight- I ly exceeds thevalue a its normally closed port will open slightly, and in sodoing willadmit a small amount of air around. the initial source flowing throughthe restriction 24. The auxiliary air pressure admitted to the top ofvalve F, caused by the flow of air through the slightly open normallyclosed seat of valve F, increases the opening of this seat stillfurther, thereby admitting more air and hence opening the normallyclosed seat of valve F still further. This regenerative cycle causes thepressure on the diaphragms of pilot valves E, F and G to abruptly riseto the source pressure value. This increase in pressure on thediaphragms of valves E, F and G occurs along the line CD' of Fig. 3instead of slowly reaching the same value along the line CD" of Fig. 3.

shut ofivwhen its top is pressurized.

When the diaphragm of pilot valve E is pressurized,

its normally open seat 22 closes and its normally closed seat 29 opensto atmosphere. The pressure on the dia-' phragms of pilot valves A and Bis thereby vented to atmosphere through the common port 23 of valve Eand its now open seat 29.

De-pressurizing the diaphragm of pilot valve A causes seat 4 to close.When seat 4 closes, the auxiliary air sup- :ply is eliminated and thepressure trapped between the i As the .diaphragm of pilot valve A isde-pressurized,

so also is that of pilot valve B, thereby causing its normally closedseat to close and its normally open seat to open. Since the diaphragm ofpilot valve C is pressurized, the return to normal position of pilotvalve B establishes communication for the trapped pressure in the timingcirouit to the adjustable restriction 25. Such communication isestablished through the common port and normally open seat of valve Band through the common port and the now open normally closed seat ofpilot valve C.

-'I'he;-pressure in the timing section down-stream of the 'its' normallyopen seat 5 to open and its normally closed 7 common port of valve B,will therefore diminish along a line DE' of Fig. 3, the rate of pressuredecrease depending on the timing circuit volume and the area of therestriction or orifice 25.

When the trapped pressure in the timing circuit reaches a valueindicated at a in Fig. 3, the normally open seat of pilot valve C justbegins to open and its normally closed seat just begins to close. Withthe slight opening of the normally open seat of valve C, air pressure isbled olf from the timing circuit more rapidly since the restriction 25is by-passed. As a result, the decreased pressure on the diaphragm ofpilot valve C causes it to open, its normally open port wider until thecircuit is degeneratively de-pressurized in an abrupt manner along theline E'F of Fig. 3.

To aid in the degenerative action, the pilot valve D exhibits similarcharacteristics to those just described with reference to valve C. Thedual action of pilot valves C and D thus cause an instantaneous drop inthe timing circuit pressure.

Since the timing circuit pressure is also exerted on the diaphragms ofpilot valves G and E, they too will snap to their depressurizedpositions as the timing circuit pressure drops. The air on the diaphragmof process valve H will therefore be vented to atmosphere in an abruptmanner through the common port and the now open normally open seat ofpilot valve G. Process valve H will thereupon be snapped closed.

Fig. 4 illustrates a graph or chart of the pressure on the diaphragm ofthe process valve H. The time interval T T measures the time lapsebetween the closure of the normally open seat of valve D and the openingof the normally closed seat of valve G. The length of this timing periodis dependent on the size of restriction 24 and upon the total volume ofthe timing circuit portion of the system. During the time interval T Tthe process valve H will be pressurized and the length of this intervalwill depend upon the adjusted size of restriction 25 and upon the timingcircuit volume, as previously mentioned. Because of the degenerativeaction resulting from the return of valves C and D to theirde-pressurized positions, the process valve H is abruptly de-pressurizedat the end of the T T interval. The system connected as described inFig. 2 thus provides an initial delay (T T adjustable by means ofrestriction 24, and a period (T T during which process valve H ispressurized, adjustable by means of restriction 25. The pressure riseand decline in process valve H occurs abruptly, rather than followingthe exponential curves A and B of Fig. 1.

The system of Fig. 2. has additional flexibility in providing alternateload connections. For example, if the diaphragm of the load pilot valveG is placed in parallel with the diaphragms of pilot valves A and B byconnecting it to alternate load connection 36 in Fig. 2, it 'will beobvious that the resulting sequence of pressurization of process valve1-1 will be as shown in Fig.5. Under these conditions the process valveH will be pressurized and de-pressurized between times T and T It mayalso be shown that if the diaphragm of load pilot valve G is placed inparallel with the diaphragms of pilot valves C and D, by connecting itto alternate load connection 35 of Fig. 2, the resulting sequence 'willoccur as shown in Fig. 6. The process valve H will under theseconditions be pressurized and de-pressurized between times T and T Thepresent invention thus provides a non-electrical system for controllinga load, such as process valve H, that produces a snap action in the loadvalve instead of 4 the throttling action conventionally characteristicof pneumatic or hydraulic systems. The regenerative and degenerativeeffects produced by the pilot valves might be applied to controlcircuits of differing configuration and the specific example describedis to be construed as illustrative only, the invention being limitedonly by the appended claims.

The invention claimed is:

1. In combination in a pneumatic control system, a valve with a valveseat and a valve member adapted to alternately open and close, withinlet and outlet ports communicating, respectively, with the two sidesof said seat, and with pressure responsive means actuating said valvemember; and means for rapidly actuating said valve comprising anunrestricted duct communicating with one of said ports, the other ofsaid ports communicating with said pressure-responsive means, and arelatively restricted duct containing a predetermined volumecommunicating in shunt with said ports.

2. In a pneumatic control system having a pressure source and apressure-responsive utilization device, two parallel lines between saidsource and said device, one line containing a series-connectedconstriction, and the other line containing a normally closed port of apressureresponsive valve, and a feed-back line from the downstream sideof said normally closed port to the pressureoperating chamber of saidvalve so that operating fluid through the valve regenerativelyaccelerates opening of the valve and the operation of said pressureresponsive utilization device.

3. In a control system, a source of control pressure, a load deviceadapted to be operated upon the application of said control pressurethereto, a control pressure operated pilot valve having ports connectedbetween said source and said load device operable to apply and relievesaid control pressure on said load device, and means for operating saidpilot valve with a snap action, said means including: a restrictedpassage 'from said control pressure source to the operator for saidpilot valve, an unrestricted passage from said control pressure sourceto said pilot valve operator paralleling said restricted passage, inauxiliary pressure operated valve having its normally-closed portcontrolling said unrestricted passage, and a feedback passage from thedownstream side of said normally closed port to the operator for saidauxiliary valve, the resulting regenerative action of said auxiliaryvalve serving to operate said pilot valve with a snap action to abruptlyapply control pressure to said load device.

4. A control system as claimed in claim 3 having additional auxiliarypressure operated valve means for dis- 6 connecting both said restrictedand said unrestricted passages from said source of control pressure andventing said passages through an auxiliary restriction, and anunrestricted vent passage placed in communication with said restrictedand unrestricted passages upon operation of said auxiliary pressureoperated valve means.

5. A control system as claimed in claim 3 having additional auxiliarypressure operated valve means for disconnecting both said restricted andsaid unrestricted pas sages from said source of control pressure andventing said passages through an auxiliary restriction, an unrestrictedvent passage placed in communication with said restricted andunrestricted passages upon operation of said auxiliary pressure operatedvalve means, and means for increasing the degenerative action therebyproduced on the system including a further pressure operated valve meansproviding a further unrestricted vent passage placed in communicationwith said restricted and unrestricted passages upon operation of saidfurther pressure operated valve means.

6. A control system as claimed in claim 3 having an additional pressureoperated valve responsive to the pressure on the downstream side of saidrestricted passage, further pressure operated valve means fordisconnecting both said restricted and said unrestricted passages fromsaid source of control pressure and venting said passages through anauxiliary restriction, and an unrestricted vent placed in communicationwith said restricted and unrestricted passages upon operation of saidfurther pressure operated valve means, said further pressure operatedvalve means being operated in response to operation of said additionalpressure operated valve.

7. In combination in a control system of the class described, apressure-responsive two-position valve hav. ing two ports and a pressurechamber, a restricted passage with a measured volume communicating withsaid chamber for moving the valve after a predetermined time, and anunrestricted passage communicating with said chamber through said valveports so that fluid under pressure passing through the portsregeneratively accelerates the movement of the valve.

References Cited in the file of this patent UNITED STATES PATENTS2,427,235 Smoot Sept. 9, 1947

